Apparatus and method for fast arc extinction with early shunting of arc current in plasma

Abstract

There is provided by this invention a novel apparatus and method of operating a dc plasma process that diverts the power supply current from the plasma at the initiation of an arc, thereby inhibiting energy from flowing from the power supply to the plasma, and then to allow energy to flow again when the power supply re-enables energy flow to the plasma. The diverting means is connected to the output of the power supply to divert current away from the plasma at the initiation of an arc wherein the diverting means is actuated when the arc is detected on the output and diverts the current for a first pre-determined time. The diverting means is released at the end of the first pre-determined time before the current reaches zero wherein current is redirected to the plasma and the diverting means is reactivated at the end of a second pre-determined time in the event the arc is not extinguished.

1. Apparatus for a dc plasma process, comprising:
 a) a chamber for plasma processing; 
 b) a power supply having an output capacitor for supplying voltage to the chamber to ignite a plasma and deliver power; 
 c) a shunt switch disposed between the power supply and the chamber to divert current away from the plasma at an initiation of an arc; and 
 d) a blocking diode connected to an output terminal of the shunt switch to isolate the output capacitor from the shunt switch. 
 
   
   
     2. Apparatus for a dc plasma process as recited in  claim 1  wherein the actuation of the shunt switch occurs after the arc is detected, and diverts the current for a first predetermined time interval. 
   
   
     3. Apparatus for a de plasma process as recited in  claim 2  wherein the shunt switch is released at the end of the first predetermined time interval before current in the plasma reaches zero, wherein current is redirected from the power supply to the plasma. 
   
   
     4. Apparatus for a de plasma process as recited in  claim 3  wherein the shunt switch is reactivated at the end of a second predetermined time interval in the event the arc is not extinguished. 
   
   
     5. Apparatus for a dc plasma process, comprising:
 a) a chamber for plasma processing; 
 b) a power supply for supplying voltage to the chamber to ignite plasma and deliver power; 
 c) a shunt switch in parallel with an output capacitor of the power supply to divert current away from the plasma at an initiation of an arc; and 
 d) a dc source in series with the shunt switch wherein the dc source provides a voltage that aids in extinguishing the arc. 
 
   
   
     6. Apparatus for a do plasma process as recited in  claim 5  wherein a diode is connected in series with the shunt switch such that the diode is forward biased when the shunt switch is diverting current. 
   
   
     7. Apparatus for a dc plasma process as recited in  claim 6  wherein actuation of the shunt switch occurs after the arc is detected, and diverts the current for a first predetermined time. 
   
   
     8. Apparatus for a dc plasma process as recited in  claim 7  wherein the shunt switch is released at the end of the predetermined time interval before current in the plasma reaches zero, wherein current is redirected from the power supply to the plasma. 
   
   
     9. Apparatus for a de plasma process as recited in  claim 8  wherein the shunt switch is reactivated at the end of a second predetermined time in the event the arc is not extinguished. 
   
   
     10. A method of operating a dc plasma process comprising:
 a) delivering voltage, current and power from a set of at least two output terminals of a power supply to a plasma chamber to ignite and sustain a plasma, the power supply having stored energy; 
 b) sensing an arc condition in the plasma; 
 c) inhibiting the flow of power from the power supply to the plasma for a predetermined interruption time interval following the sensing of an arc condition; 
 d) reinstating the flow of power from the power supply to the plasma after the predetermined interruption time interval such that said stored energy is released to into the plasma; and 
 re-inhibiting the flow of power from the power supply to the plasma if an arc condition is sensed following said reinstatement of power from the power supply. 
 
   
   
     11. A method of operating a de plasma process as described in  claim 10  wherein said interruption time interval is less than 20 microseconds in duration. 
   
   
     12. A method of operating a do plasma process as described in  claim 11  wherein the step of sensing an arc condition consists of comparing a plasma voltage with a predetermined threshold value. 
   
   
     13. A method of operating a do plasma process as described in  claim 10  further comprising the steps of:
 sensing a sudden drop of plasma current, and 
 reinstating the flow of power from an inhibited power supply. 
 
   
   
     14. A method of operating a dc plasma process as described in  claim 10  further comprising the steps of:
 sensing a sudden rise in the voltage between said set of at least two output terminals, and 
 reinstating the flow of power from an inhibited power supply.